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Abstract:

A piping system comprises a resistive heating circuit, a target heating
surface, and a thermally conductive substrate adjoin (or abutting) both
the heating circuit and the heating surface. The thermally conductive
substrate can be composed of aluminum or some other material for heat
spreading. A material for heat spreading has a thermal conductivity
sufficient to evenly heat a section of the target surface within
tolerance requirements of a sensitive application. The even heating can
eliminate hot spots and cold spots of a temperature gradient along an
axis of the piping system.

Claims:

1. A method for creating thermal uniformity in a heated media delivery
system, comprising: attaching a heat sink substrate to a media carrier,
the media carrier to deliver a media; attaching a heater circuit to a
surface portion of the heat sink substrate in a manner that substantially
uniformly heats the media carrier; and mounting a temperature sensor to
the heat sink substrate.

2. The method of claim 1, further comprising: submerging the temperature
sensor into the cavity.

3. The method of claim 1, further comprising: boring a cavity into the
heat sink substrate; and submerging the temperature sensor into the
cavity.

4. The method of claim 1, further comprising: bonding the heater circuit
to the heat sink substrate,.

5. The method of claim 1, wherein the heat sink substrate is of
non-uniform thickness corresponding to non-uniform shape of the media
carrier, and an outer surface of the heat sink substrate is of uniform
thickness.

6. The method of claim 1, wherein the media carrier is composed of
PFA-type plastic.

7. The method of claim 1, wherein the media carrier is composed of
stainless steel.

8. The method of claim 1, wherein the heater circuit includes a pattern
that has hot and cold spots during operation.

9. The method of claim 1, further comprising: providing a feedback signal
from the temperature sensor to a heater control that adjusts the heater
circuit accordingly.

10. The method of claim 1, wherein the media comprises at least one of a
gas, a liquid, or a mobile solid.

11. A piping member to create thermal uniformity in a heated media
delivery system, comprising: a heat sink substrate attached to a media
carrier, the media carrier to deliver a media; a heater circuit attached
to a surface portion of the heat sink substrate in a manner that
substantially uniformly heats the media carrier; and a temperature sensor
mounted to the heat sink substrate.

12. The piping member of claim 11, wherein the temperature sensor is
submerged into the heat sink substrate.

13. The piping member of claim 11, wherein a cavity is bored into the
heat sink substrate, and the temperature sensor is submerged into the
cavity.

14. The method of claim 1, wherein the heater circuit is bonded to the
heat sink substrate.

15. The piping member of claim 11, wherein the heat sink substrate is of
non-uniform thickness corresponding to non-uniform shape of the media
carrier, and an outer surface of the heat sink substrate is of uniform
thickness.

16. The piping member of claim 11, wherein the media carrier is composed
of PFA-type plastic.

17. The piping member of claim 11, wherein the media carrier is composed
of stainless steel.

18. The piping member of claim 11, wherein the heater circuit includes a
pattern that has hot and cold spots during operation.

19. The piping member of claim 11, further comprising: a heater control
to receive a feedback signal from the temperature sensor, the heater
control adjusting the heater circuit accordingly.

20. The method of claim 1, wherein the media comprises at least one of a
gas, a liquid, or a mobile solid.

[0003] Embodiments of the invention relate generally to a heating circuit,
and more specifically, incorporating a thermally conductive substrate
between the heating circuit and a target heating surface.

[0004] 2. Prior Art

[0005] Piping and weldment systems that must operate at higher than
ambient temperatures are typically heated using some sort of electrical
resistance heater circuit. These circuits are held in close proximity to
the target surfaces, and are typically insulated using some material
wrapped around the outside, such as silicone rubber or fiberglass. In
industrial applications, this insulation material serves several purposes
including physical protection of the heater circuit from the environment,
improving electrical and thermal efficiency by reducing thermal losses to
the environment, increasing heater circuit life by reducing the chance of
over-temperature and failure of the electrical resistance material, and
improving personnel safety by reducing the touch temperature on the
outside surface of the heated system.

[0006] Certain materials with low thermal K factors used as insulation
will improve the above effects, but heat losses and thermal loading of
the piping system and the components included in the system will effect
the thermal uniformity from one point in the system to another, and
unless the insulation is "perfect," it alone is insufficient to provide
the thermal uniformity across the system that is required in the
semiconductor industry. The difference from high to low temperature
across a system becomes worse as the operating temperature set point
increases. Additionally, lack of thermal uniformity is compounded by the
imperfection of the heater resistance element due to it's inherent hot
and cold spots.

[0007] Electrical resistance heaters utilize a heat sink to be closely
engaged with the heater surface for proper operation and longest service
life. If the heater is allowed to operate in "open air," it can overheat
and fail much more quickly than if it is in intimate thermal contact with
a heat sink. This accelerated failure mechanism becomes more prevalent as
the operating temperature set point increases, especially as the thermal
limits of the materials employed in the assembly are approached.

[0008] In high tech industries such as the semiconductor manufacturing
sector, much finer uniformity is often required, with typical
expectations on the order of plus or minus five degrees C. at a set point
of up to 200 degrees C. Though it may be theoretically possible to
achieve this level of uniformity using traditional heater construction
methods, several iterations of the design may be required and the results
lack manufacturing repeatability. Additionally, traditional heater
construction often lead to very complex heater system design and finely
controlled thermal balancing that can be affected by and thrown off by
unpredictable changing environmental conditions.

[0009] Additionally, high tech industries are demanding that heated
systems operate at higher and higher temperatures, often pushing the
envelope for materials capability.

[0010] Thermal system designers require better methods for protecting the
heaters, especially at higher operating temperature ranges, and for
creating the desired high level of thermal uniformity.

SUMMARY

[0011] The above-mentioned needs are met by a method, article of
manufacture, and a method of manufacturing for incorporating a thermally
conductive substrate between an electrical resistance heater and a target
heating surface for uniform heating.

[0012] In one embodiment, a piping system comprises a resistive heating
circuit, a target heating surface, and a thermally conductive substrate
adjoining (or abutting) both the heating circuit and the heating surface.
The thermally conductive substrate can be composed of aluminum or some
other material for heat spreading.

[0013] In another embodiment, a material for heat spreading has a thermal
conductivity sufficient to evenly heat a section of the target surface
within tolerance requirements of a sensitive application. The even
heating can eliminate hot spots and cold spots of a temperature gradient
along an axis of the piping system.

[0014] In yet another embodiment, an insulator surrounds a surface of the
heating circuit.

[0015] In still another embodiment, the heating circuit increases a
temperature of gas or fluid being transported through the piping system.

[0016] The features and advantages described in this summary and in the
following detailed description are not all-inclusive, and particularly,
many additional features and advantages will be apparent to one of
ordinary skill in the relevant art in view of the drawings,
specification, and claims hereof. Moreover, it should be noted that the
language used in the specification has been principally selected for
readability and instructional purposes, and may not have been selected to
delineate or circumscribe the inventive subject matter, resort to the
claims being necessary to determine such inventive subject matter.

BRIEF DESCRIPTION OF THE FIGURES

[0017] In the following drawings like reference numbers are used to refer
to like elements. Although the following figures depict various examples
of the invention, the invention is not limited to the examples depicted
in the figures.

[0018] FIG. 1 is a schematic diagram showing a cross-section view of a
pipe, perpendicular to an axis, having a thermally conductive substrate,
according to an embodiment of the present invention.

[0019] FIG. 2 is a schematic diagram showing a cross section view of a
pipe, along an axis, having a thermally conductive substrate, according
to an embodiment of the present invention.

[0020] FIG. 3 is a chart illustrating a heating gradient of a conventional
pipe of the prior art compared to a heating gradient of a piping system
having a thermally conductive substrate, according to an embodiment of
the present invention.

[0021] FIG. 4 is a flow chart illustrating a method for creating thermal
uniformity in a heated media delivery system, according to an embodiment
of the present invention.

DETAILED DESCRIPTION

[0022] A method, an article of manufacture, and a method of manufacturing,
is disclosed, for incorporating a thermally conductive substrate between
an electrical resistance heater and a target heating surface. By
employing this method, electrical resistance heaters can operate more
safely at higher temperatures, with more uniformity, and system thermal
uniformity is greatly enhanced. The following detailed description is
intended to provide example implementations to one of ordinary skill in
the art, and is not intended to limit the invention to the explicit
disclosure, as one of ordinary skill in the art will understand that
variations can be substituted that are within the scope of the invention
as described.

[0023] FIG. 1 is a schematic diagram showing a cross-section view of a
pipe 100 (or weldment system), perpendicular to an axis, having a
thermally conductive substrate according to an embodiment of the present
invention. The pipe can be used to transport a heated media 110 (or a
substrate) such as gas, fluid, or mobile solids. A heat sink substrate
120 (or thermally conductive substrate) transports heat from a
resistance-style heater 130 (or resistance heating circuit) to a heated
media (or target heating surface such as a media carrier composed of
PFA-type plastic or stainless steel). In one embodiment, the
resistance-style heater 130 is a thermocoupler.

[0024] The pipe 100 is heated to mitigate condensation within the lines,
for more uniform delivery of the substance. The pipe is adapted for use
in sensitive applications, such as a clean room in which delivery of
gaseous doping agents in CVD, MOCVD or LPCVD processes, wafer cleaning
processes, are used in the manufacture of LEDs, LCDs and other
components. This application is particularly sensitive due to the
microscopic size of electrical circuits generated in a clean room which
have a low tolerance for variations in media temparture. Other exemplary
implementations include medical applications, such as heated PFA lines
and tubing for dialysis machines, and a thermal angel for a blood
transfusion. One of ordinary skill in the art will recognize that many
other applications are possible.

[0025] In some embodiments, the pipe 100 is a section of a piping system.
A piping specialist can modify an off-the shelf the pipe. Also, a
manufacturer can assemble and produce the pipe 100 as a finished product.
These modified pipes can then be delivered on-site and installed for a
particular application.

[0026] FIG. 2 is a schematic diagram showing a perspective view of a pipe
200 with a heater assembly, along an axis, having a thermally conductive
heat sink substrate 210 according to an embodiment of the present
invention. Both horizontal and vertical cross-sections are shown in the
perspective view. In one embodiment, a heat sink substrate 210 does not
have a uniform thickness. Therefore, the heater substrate can be built to
conform to non-uniform surfaces and ensure that they are heated evenly.

[0027] In some embodiments, an outer surface of the pipe 200 is
substantially even despite the non-uniformity of the inner surface. The
inner surface can be uneven as a result of a joint between two members,
or an elbow. Also, circumference can change in order to create an
increased or reduced pressure on the media.

[0028] A thermocouple 240 is embedded in the heat sink substrate 210. A
hole can be bored during retrofitting of an off the shelf pipe, or
pre-bored during manufacture. By moving the thermocouple 240 away from
the resistance-style heater 220, a better temperature reading is taken.
Additionally, an epoxy can be used to backfill a boring cavity, for an
even better temperature reading.

[0029] In one embodiment, the resistance-style heater 220 is permanently
bonded directly to a substrate. As a result, the resistance-style heater
220 remains engaged with a heat sink in a manner that eliminates
hot-spots along the heater circuit. Additionally, an expected service
life of the heater circuit can be extended. A heater control (not shown)
can receive a feedback signal from the thermocouple 240 and adjust the
resistance-style heater 220 as needed to maintain a target temperature.

[0030] In one embodiment, insulation 230 is then used around the outside
of the heater for physical protection of the resistance-style heater 220
and for plant safety and to prevent heat loss. But the insulation 230
becomes less important to creating thermal uniformity than is the case in
a system without a substrate.

[0031] In another embodiment, a substrate is custom-shaped to conform to a
target surface. For example, an inside diameter of the substrate to
exactly conform to the outside diameter of the target piping system (see
FIG. 1) This system is designed in a clam-shell arrangement that is
clamped around the outside of the target piping or weldment system,
allowing easy removal for system repair or maintenance.

[0032] FIG. 3 is a chart illustrating a comparison of heating gradients.
Line 301 represents a conventional piping system while line 302
represents a piping system having a thermally conductive substrate. As
can be seen, the dramatic hot and cold spots of line 301 are
substantially eliminated or reduced in line 302. Thus, the improved
piping system of line 302 is far more uniform and predictable. In one
embodiment, when employed in a high-tech fluid or gas delivery system,
the piping system will meet the required design criteria for both
temperature control and thermal uniformity. One important design criteria
can be related to temperature variation along an axis of the piping
system.

[0033] Improvements in thermal uniformity are dramatic and instantly
recognizable. In FIG. 3, the thermal profile across a typical heated
weldment piping system employing traditional electrical resistance heat
with silicone-rubber insulation is shown in line 301. Large peaks and
valleys were measured, which correspond to hot spots along the heater
circuit and to cold spots in the flow path. These hot spots represent
likely failure points as the electrical resistance heater can be driven
beyond the material's safe operating temperature, and the cold spots
represent locations where the conditions of the process fluids flowing
through the piping system could fall below the desired operating band.

[0034] Another advantage to this design approach is that since the thermal
profile is flattened across the entire heated system, thermal performance
is more predictable and accurate thermal models can be created. This
allows the system designer to create custom thermal profiles, such as a
system with one end or portion colder than another.

[0035] In one embodiment, the piping system is used for applications with
relatively tight tolerance levels, such as semiconductor processing.
Precise and linear thermal gradients can be created using this approach,
allowing a predictable rise from one target temperature to another within
a system. When using conventional heating methods this sort of
flexibility is only possible by employing multiple control zones,
sophisticated temperature controllers, and accepting the wide uniformity
swings inherent to conventional heating methods.

[0036] FIG. 4 is a flow chart illustrating a method 400 for creating
thermal uniformity in a heated media delivery system, according to an
embodiment of the present invention.

[0037] At step 410, a heat sink substrate is attached to a media carrier
that delivers a media such a gas, liquid, or a mobile solid.

[0038] At step 420, a heater circuit is attached to a surface portion of
the heat sink substrate in a manner that substantially uniformly heats
the media carrier. In turn, the substance itself is substantially
uniformly heated as well.

[0039] At step 430, a temperature sensor is mounted. The temperature
sensor can be mounted to allow a more uniform reading of the temperature.
In particular, some temperature sensors are typically mounted with the
heating element. The heating element has different contours of hot and
cold spots depending how far away the temperature is from a wire carrying
the heat.

[0040] In one implementation of the current invention, a hole is bored
within heat sink substrate. By placing probes of the temperature sensor
within the bored holes, away from hot and cold spots, a more accurate
temperature reading is taken. The temperature reading is less affected by
whether the heater circuit is currently heating or cooling, and by coil
patterns of the heater circuit. In still another embodiment, the bored
hole is then backfilled with an epoxy or other suitable substance to
remove any air pocket that may introduce inaccuracies to the temperature
reading.

[0041] Example Specifications:

[0042] In one embodiment, electrical resistance heater insulated with
silicone rubber, Kapton polyimide, polyester film or any other
appropriate electrical insulator. Operating temperature range is from
ambient to approx. 300 degrees C.

[0043] Substrate material can be Aluminum or Aluminum alloys, Copper or
copper alloys, carbon fiber, thermally conductive plastic or other
thermally conductive rigid or semi-rigid material suitable to the
required temperature range of the system.

[0044] Insulation can be made from silicone rubber, fiberglass, polyimide
or other materials as required by physical and thermal design criteria.

[0045] Electrical power requirements can be anything required by the
application. Typical voltage range is 12 VDC to 240 VAC, and typical
power ranges from fractional wattage to hundreds of watts.

[0046] Measurement and control is accomplished using integrated
temperature sensors, thermostats, thermal fuses and other devices as
required by the application.

[0047] As will be understood by those familiar with the art, the invention
may be embodied in other specific forms without departing from the spirit
or essential characteristics thereof. Likewise, the particular naming and
division of the portions, modules, agents, managers, components,
functions, procedures, actions, layers, features, attributes,
methodologies and other aspects are not mandatory or significant, and the
mechanisms that implement the invention or its features may have
different names, divisions and/or formats.

[0048] Accordingly, the disclosure of the present invention is intended to
be illustrative, but not limiting, of the scope of the invention.